1. Field of the Invention
The present invention relates to scavenging of sulfur species, and more particularly to use of particular imines for scavenging such species as sulfides and elemental sulfur from petroleum-derived media.
2. Description of the Prior Art
Petroleum-derived media, such as crude oil, residuum, various refinery fractions and finished fuels, often contain hydrogen sulfide or elemental sulfur or both. The presence of these sulfur species creates a variety of problems. For example, hydrogen sulfide is a very toxic gas, with a disagreeable "rotten egg" smell. Its liberation from a medium in which it is dissolved, for example, during storage or transport of the medium can raise serious environmental and health problems.
In response to such problems, a variety of hydrogen sulfide scavengers have been developed. For example, U.S. Pat. No. 5,169,411 to Weers, a co-inventor herein, describes a class of such scavengers for crude, residua and petroleum fuel media. These scavengers inhibit liberation of hydrogen sulfide from the media, generally by reaction with the hydrogen sulfide to form a new sulfur compound that is resistant to evolution as a gas. Preferably, the new sulfur compound is stable at high temperatures so that inhibition of hydrogen sulfide liberation is maintained even in high temperature situations. Moreover, it is, of course, desirable that such characteristics be associated with a scavenger that is inexpensive to manufacture.
However, the presence of other sulfur species besides hydrogen sulfide raises serious problems as well. Thus, the presence of elemental sulfur in a fluid can cause corrosion of metals contacted by the fluid. For example, fuels often contain elemental sulfur, and in fuels such as gasoline, the elemental sulfur attacks the copper commutator of fuel pump motors contacted by the gasoline, leading to early wear of the commutator. Accordingly, agents that scavenge elemental sulfur as well as hydrogen sulfide are desired.
Nevertheless, it has been found that efficacy in scavenging hydrogen sulfide is not indicative of scavenging efficacy with respect to other sulfur species such as elemental sulfur. For example, a commercial product that corresponds to that of Test 10 of U.S. Pat. No. 5,169,411 has been found to be ineffective in scavenging elemental sulfur, or at least not nearly as effective as desired. Not only that, but the noted commercial product has been found to have an offensive odor, making its handling troublesome and its use undesirable in many situations. Yet, other conventional scavengers are so far from ideal that the superior hydrogen sulfide scavenging efficacy and other desirable characteristics of the scavenger of that Test 10 make it a popular scavenger in the petroleum refining industry despite those drawbacks.
As shown by U.S. Pat. Nos. 4,149,966 and 5,336,277, scavengers directed specifically to elemental sulfur also have been developed. However, scavenging such as by the methods of those patents involves addition of even more sulfur species (organomercaptans), which is undesirable, particularly in view of the offensive smell typically imparted to compositions by addition of mercaptans. Moreover, at least in the case of U.S. Pat. No. 4,149,966, scavenging is not accomplished by simple addition of a chemical scavenger. Rather, further process steps and equipment are required. Also, prior art additives for scavenging elemental sulfur may produce hydrogen sulfide, therefore requiring addition of a hydrogen sulfide scavenger in addition to the elemental sulfur scavenger.
Therefore, industries have continued their searches for ever better scavengers having desirable handling characteristics, including a non-offensive odor, low cost, high efficacy in scavenging elemental sulfur as well as hydrogen sulfide, and the capability of inhibiting evolution of hydrogen sulfide even at high temperatures.